The invention relates to tire uniformity, and more specifically to a method for analyzing and controlling the uniformity of tires during tire manufacturing.
Tire non-uniformity relates to the symmetry (or lack of symmetry) relative to the tire's axis of rotation in mass, geometric, or stiffness characteristics. Conventional tire building methods unfortunately have many opportunities for producing non-uniformities in tires. During rotation of the tires, non-uniformities present in the tire structure produce periodically-varying forces at the wheel axis. Tire non-uniformities are important when these force variations are transmitted as noticeable vibrations to the vehicle and vehicle occupants. These forces are transmitted through the suspension of the vehicle and may be felt in the seats and steering wheel of the vehicle or transmitted as noise in the passenger compartment. The amount of vibration transmitted to the vehicle occupants has been categorized as the “ride comfort” or “comfort” of the tires.
Tire uniformity characteristics, or attributes, are generally categorized as dimensional or geometric variations (radial run out and lateral run out), mass variance, and rolling force variations (radial force variation, lateral force variation, and tangential force variation, sometimes also called longitudinal or fore and aft force variation).
The art includes different methods for measuring uniformity in tires. Typically, rolling force variations are measured as the spindle force and moment variations of a tire and wheel assembly rotating under load against a road wheel or track. Geometric variations are usually measured as deviations from an average dimension. Mass variance measurement is typically limited to mass imbalance, which is the first harmonic component of mass variance. Mass imbalance may be measured statically on a balance device or on a device that rotates the tire with respect to an axis passing through the geometric center of the tire without applying a load to the tire.
Measurement of non-uniformities is typically done for quality control after manufacturing the tire to determine the effect the non-uniformities will have on a vehicle, that is, the vibrations that will be produced by the non-uniformities. The measurement can be used, for example, to reject tires or to sort or grade tires according to the vehicle for which the tire will be used, if relevant values for the measured variations can be determined.
A difficulty in evaluating non-uniformity measurements is that force variations are derivative of one or more underlying physical non-uniformities such as joint overlap, cord spacing, and tread gauge. Force variations may also be related to other measurements such as the geometric run out measurements. Thus, error may be introduced in the evaluation of the force variations unless the interaction inter-relations among variables are taken into account.
Another difficulty is in the actual measurement and evaluation of the force variations caused by tire non-uniformities. The magnitude of force variations often is a function of the speed of rotation of the tire, and thus, to completely measure the force variation would require the tester to rotate and measure the tires at a variety of speeds. While it is possible to test tires throughout a range of relevant speeds, it is expensive and time-consuming to do so.
Another difficulty in actual high speed measurement is that at high speed rotation the measurement data includes noise associated with the hardware and software used to make the measurements, for example, machine resonance, tire/wheel mounting aberrations, transducer calibration error and cross-talk between transducers, and limitations of the sampling and averaging procedures. Generally, testing at low rotation speeds is simpler and less expensive than testing at high rotation speeds.
To avoid using exhaustive testing protocols, some working in the art have devised methods for using low rotational speed measurements to predict the force variations at high rotational speeds. British patent publication no. 1,212,701 by Gough relates the changes in effective rolling radius at low speed to the tangential force variation (fore and aft) at high speed. U.S. Pat. No. 4,815,004 to Beebe relates changes in effective rolling radius, and derivative measurements, acceleration of the tread surface, angular acceleration, and acceleration of the load wheel relative, to the angular acceleration of the tire to the tangential force variation at high speed. In both these publications, tangential force variation is stated to be the main cause of steering wheel vibrations at high speed. U.S. Pat. No. 5,396,438 to Oblizajek uses variations in two low speed measurements selected from the set of effective rolling radius, radial force variation, geometric run out and tangential force variation to predict tangential force variation at high speed.
These methods have an important limitation related to the selection and handling of the tire attributes. The attributes to be tested and the attribute to be predicted are selected and fixed, and are not evaluated for importance for the particular structure of the subject tire.
In these methods, the attributes are also treated as if each is totally independent of any other attribute, which can lead to errors if, in fact, the selected attributes overlap, that is, are to some degree coherent.
The present inventor has discovered that by measuring a plurality of tire attributes at low speed and first evaluating the attributes for relevance in predicting one or more high speed attributes, an improved method of predicting high speed uniformity attributes is obtained.
In addition, one aspect of the invention relates to using the information derived from evaluating the slow speed attributes to identify and control aspects of the manufacturing process that may be producing the non-uniformities.
According to the invention, a method of analyzing and controlling uniformity during tire manufacture comprises the steps of selecting at least one target attribute and assigning a target value thereto, measuring the target attribute in a subject tire at a first rotational speed approximating highway speed, measuring a plurality of indicator attributes in the subject tire at a second rotational speed lower than the first rotational speed, determining a plurality of predictors for each at least one target attribute, each predictor including at least one of the indicator attributes, selecting a predictor from the plurality of predictors, measuring indicator attributes of the selected predictor in an additional subject tire at the second rotational speed, predicting a value for the target attribute based on the selected predictor for the additional subject tire, and comparing the predicted value of the target attribute to the target value.
According to another aspect of the invention, the method further comprises the steps of comparing the measured indicator attributes making up the selected predictor to limit values for the indicator attributes to determine a deviation therebetween, identifying manufacturing operation related to the deviation, and responsive to the comparison, controlling the identified manufacturing operation to correct the deviation for at least an additional subject tire.
According to the invention, the target attribute is a tire force and/or a tire moment response produced during rotation of the tire, for example, radial force variation, tangential force variation, lateral force variation, or self-aligning moment variation, that has been identified as being of interest. The indicator attributes include mass variance, geometric variance measurement, and a force response produced during rotation of the tire.
According to another aspect of the invention, the method includes the step of sorting tires responsive to the comparison of the predicted value to the target value.
According to yet another aspect of the invention, the method includes the step of determining a plurality of predictors includes condensing the set of indicator attributes to remove overlap, that is, coherence, in the measured data, and determining a ranking of importance of the condensed indicator attributes to predicting the target attribute.
These and other aspects and embodiments of the invention will become better understood by reference to the following detailed description.